A .lamda./2 resonator comprises an inner conductor formed hole having an
inner conductor with both open-ends, formed therein, and .lamda./4
resonators comprise inner conductor formed holes having inner conductors
with one short-circuited ends and the other open ends, respectively. The
resonators are coupled, whereby a terminal electrode connected to the
vicinity of the one open end of one of the .lamda./4 resonators functions
as an unbalanced terminal, and terminal electrodes connected to both open
ends of the .lamda./2 resonator function as balanced terminals.